The invention relates to a method for adjusting the braking torque of a permanently excited magnetic hysteresis brake by means of a mechanically acting actuator and a permanently excited magnetic hysteresis brake for carrying out such method.
Hysteresis brakes allow a uniform tension to be maintained without acting on the yarn with a friction which can damage the yarn. The yarn passes through the magnetic hysteresis brake at a predetermined speed. The yarn is thus guided via a roller, with it completely or partially looping the roller and being acted upon by the braking action of the magnetic hysteresis brake. The braking torque is independent of the rotational speed.
Hysteresis brakes are used in the textile industry, for example in the production of twisted yarn or the winding of yarn on bobbins.
German Patent Publication DE 19705290 A1 describes a permanent magnet-excited hysteresis brake with a roller, a hysteresis ring and a magnetic ring provided with magnetic poles. The hysteresis ring is rotationally fixed to the roller. The magnetic ring is fastened to a support part, which is axially displaceably mounted relative to the hysteresis ring by means of an adjusting device. The adjusting device comprises a thread attachment on the support part and a threaded spindle on an adjusting ring, which is axially fixed, but rotatable. By rotating the adjusting ring, the magnetic ring is displaced relative to the hysteresis ring. The displacement brings about a change in the braking torque of the hysteresis brake. The axial arrangement of the roller is adjusted by means of a central screw, which presses the roller against a central axial spring. The rotation of the screw allows a basic adjustment of the immersion depth of the magnetic ring in the hysteresis ring and therefore a calibration of the hysteresis brake. With the hysteresis brake from German Patent Publication DE 19705290 A1 it is necessary for the adjustment of the braking torque for the operation and for the adjustment of the braking torque during the calibration, to keep in readiness and actuate two different adjusting devices.